Warped Doors
Properly installed and without error, a door in its frame should be able to swing freely and latch without sticking at any point. However, with time or even right after installing a door, you may notice the slab misaligning with the jamb. The door may no longer seal properly, or other issues arise with the door swing. One cause for this may be the door itself due to warping of the slab. Warping can be seen in almost any wooden door and is more common in older and taller slabs. This article explains why a door slab may warp, and how to determine whether your slab is warped.
How Do Doors Warp?
   A door slab can warp in a variety of ways:
Bowing
A consistent curve along the door's height.
Cupping
Similar to bowing, but along the door's width.
Twisting
One or more corners of the door warps away from the others.
   These transformations happen for a variety of reasons. One of the most common reasons is due to the slab's environment. Excessive heat or humidity creates moisture variations within and around the door, causing the door to expand. The door can take on water and swell, and if this occurs rapidly, the wood could even split. The door's finishing may also be incomplete, meaning the wooden components aren't sealed and can more easily take on moisture.
How Do I Check if My Door is Warped?
Fortunately, the most common way to check if your door is warped is also the simplest. Known as the string method, this is a quick way to assure a slab is true with only a length of string. Follow the steps below on each side of your slab to check for warping. Depending on the type of door, the gap may be larger or smaller; for example, a larger door will be permitted a larger gap. This test can also be performed with a long straightedge by placing the straightedge against the door and inspecting for a gap.
Step 1:
Tape or hold a length of string against the bottom of the door to be tested.
Step 2:
Wrap the string around the underside of the door and pull it up and down the top of the door, making sure the string remains taut.
Step 3:
Inspect the gap between the door and the string at the lockset. The gap should be consistent along the length of the door. Refer to your door's warranty for acceptable tolerances.
The string test done on the convex side of the slab will be inconclusive, as the string lies against the door. Make sure to test both sides of your slab.
When done correctly, a gap between the door and string should appear. Take a measurement at the center of the slab and string.
What if my Slab Isn't Warped?
   If the string method shows your slab isn't warped, there could be other issues causing problems with your entryway. Instead of the door, the frame itself may be warped. The frame could also be incorrectly installed or uneven. Once the frame is placed in the rough opening, it should be evaluated with a level to assure it is plumb, level, and square. If any of these are lacking, the door will not be smooth to operate.
If the frame and slab aren't the issue, then the hinges may be unaligned, or if the problem arises after time, the home itself could be shifting. A trained contractor will be able to identify and correct most entryway issues.
